1. Field of the Invention
The present invention relates to soft magnetic films used as core materials of thin-film magnetic heads. In particular, the present invention relates to a soft magnetic film which is composed of an FeCoxcex1 alloy wherein xcex1 represents a noble metal, which has a saturation magnetic flux density Bs of at least 2.0 T, and which exhibits high corrosion resistance. Also, the present invention relates to a thin-film magnetic head including the soft magnetic film, a method for making the soft magnetic film, and a method for making the thin-film magnetic head.
2. Description of the Related Art
For future higher-density recording, for example, a magnetic material having a high saturation magnetic flux density Bs must be used as a core layer of a thin-film magnetic head to increase the recording density by concentrating the magnetic flux to the vicinity of the gap of the core layer.
A traditionally used magnetic material is a NiFe alloy. The NiFe alloy film is formed by electroplating using a continuous DC and exhibits a saturation magnetic flux density Bs of about 1.8 T.
Although future higher-density recording requires a soft magnetic film having a higher saturation magnetic flux density Bs, the NiFe alloy does not sufficiently meet such a requirement.
Another soft magnetic material often used, other than the NiFe alloy, is an FeCo alloy. The FeCo alloy film having an optimized composition has a higher saturation magnetic flux density Bs than that of the NiFe alloy film, and also has the following problem.
In some configurations of thin-film magnetic heads and other magnetic elements, a NiFe alloy film is disposed on the FeCo alloy film by electroplating. Unfortunately, the FeCo alloy film is dissolved and corroded by ionization during the electroplating.
It is likely that a large potential difference (standard electrode potential difference) is generated between the FeCo alloy film and the NiFe alloy film and causes dissolution of the FeCo alloy film by the galvanic effect.
In a single FeCo alloy film configuration, this film must have high corrosion resistance during the manufacturing processes of thin-film magnetic heads and other magnetic elements. For example, the film must have high corrosion resistance during milling steps of sliders and cleaning steps of the elements. Also, the film must have high corrosion resistance in actual operating environments of thin-film magnetic heads.
Accordingly, in the plating of the NiFe alloy on the soft magnetic film, the soft magnetic film must have a high saturation magnetic flux density Bs and high corrosion resistance.
An object of the present invention is to provide a soft magnetic film comprising an FeCo alloy which contains a noble metal xcex1 such as Pd and which has a saturation magnetic flux density Bs of at least 2.0 T and high corrosion resistance.
Another object of the present invention is to provide a thin-film magnetic head including the soft magnetic film, a method for making the soft magnetic film, and a method for making the thin-film magnetic head.
A soft magnetic film according to the present invention has a composition represented by the formula FeXCoYxcex1Z wherein xcex1 is at least one element selected from the group consisting of Rh, Pd, Pt, Ru, and Ir, wherein the ratio X/Y by mass percent of Fe to Co is in the range of 2 to 5, the xcex1 content Z is in the range of 0.5 to 18 mass percent, and X+Y+Z=100 mass percent.
The element xcex1 is added to enhance corrosion resistance. At an xcex1 content of less than 0.5 mass percent, the corrosion resistance is not enhanced. At an xcex1 content exceeding 18 mass percent, the saturation magnetic flux density Bs does not reach 2.0 T due to a decreased Fe content in the composition.
When the ratio X/Y by mass percent of Fe to Co is in the range of 2 to 5, a saturation magnetic flux density Bs of at least 2.0 T is achieved, as described in experimental results below.
The above soft magnetic film has a saturation magnetic flux density Bs of at least 2.0 T and exhibits higher corrosion resistance than that of an FeCo alloy not containing the element xcex1.
Preferably, the ratio X/Y by mass percent of Fe to Co is in the range of 2.6 to 4.3 and the xcex1 content Z is in the range of 3 to 9 mass percent.
A soft magnetic film having such a preferable composition has a saturation magnetic flux density Bs of at least 2.2 T and exhibit higher corrosion resistance than that of an FeCo alloy not containing the element xcex1.
Preferably, the soft magnetic film has a composition represented by the formula FeXCoYxcex1Zxcex2V, wherein xcex2 is at least one of Ni and Cr, the ratio X/Y by mass percent of Fe to Co is in the range of 2 to 5 and more preferably in the range of 2.6 to 4.3, the xcex1 content Z is in the range of 0.5 to 18 mass percent and more preferably in the range of 3 to 9 mass percent, the xcex2 content V is in the range of 0.5 to 5 mass percent, and X+Y+Z+V=100 mass percent.
A soft magnetic film having such a composition has a saturation magnetic flux density Bs of at least 2.0 T or at least 2.2 T under optimized conditions and exhibits higher corrosion resistance. The element xcex2 contributes to higher corrosion resistance due to the formation of a passivation film. When the element xcex2 is Ni, the film stress is decreased.
In the present invention, the soft magnetic film may be overlaid with a NiFe alloy film which is formed by plating. Thus, the resulting soft magnetic film is referred to as a composite soft magnetic film.
The noble metal element xcex1 is barely ionized alone. In the plating process of a NiFe alloy film on a soft magnetic film containing the element xcex1, the FeCoxcex1 alloy is prevented from dissolution by ionization. In an FeCoxcex1xcex2 alloy, a passivation film formed on the surface more effectively prevents the dissolution of the alloy by ionization.
In conclusion, the FeCoxcex1 alloy film and the composite soft magnetic film of the FeCoxcex1xcex2 film and the NiFe alloy film have a high saturation magnetic flux density Bs and high corrosion resistance.
The soft magnetic film according to the present invention is preferably formed by plating. A soft magnetic film having a desired thickness or a higher thickness than that by sputtering is thereby formed.
The present invention also relates to a thin-film magnetic head comprising a magnetic lower core layer, an upper core layer formed on the magnetic lower core layer with a magnetic gap provided therebetween, a coil layer for applying a recording magnetic field to the lower core layer and the upper core layer, wherein at least one of the lower core layer and the upper core layer comprises the above-described soft magnetic film.
Preferably, the thin-film magnetic head further comprises a lower magnetic pole layer on the lower core layer and at a face opposing a recording medium, wherein the lower magnetic pole layer comprises the soft magnetic film.
The present invention also relates to a thin-film magnetic head comprising a lower core layer; an upper core layer; and a magnetic pole unit provided between the lower core layer and the upper core layer, the length of the magnetic pole unit being shorter than that of the lower core layer and the upper core layer in the track width direction. The magnetic pole unit comprises a lower magnetic pole layer in contact with the lower core layer; an upper magnetic pole layer in contact with the upper core layer; and a gap layer lying between the lower magnetic pole layer and the upper magnetic pole layer, or comprising an upper magnetic pole layer in contact with the upper core layer and a gap layer lying between the upper magnetic pole layer and the lower core layer, wherein at least one of the upper magnetic pole layer and the lower magnetic pole layer comprises the above-described soft magnetic film.
Preferably, the upper magnetic pole layer comprises the above-described soft magnetic film, the upper core layer on the upper magnetic pole layer comprises a NiFe alloy and is formed by plating.
Preferably, at least one of the upper core layer and the lower core layer includes at least two magnetic sublayers at a portion adjacent to the magnetic gap or at least one of the upper magnetic pole layer and the lower magnetic pole layer includes at least two magnetic sublayers, the magnetic sublayer in contact with the magnetic gap comprising the soft magnetic film.
Preferably, the magnetic sublayer which is not in contact with the magnetic gap is formed by plating a NiFe alloy.
As described above, the FeCoxcex1 alloy and the FeCoxcex1xcex2 alloy as soft magnetic films according to the present invention has a high saturation magnetic flux density Bs of at least 2.0 T and high corrosion resistance. Thus, a thin-film magnetic head including a core layer composed of such a soft magnetic film concentrates the magnetic flux to the vicinity of the gap and is suitable for higher-density recording. The thin-film magnetic head also has higher corrosion resistance.
A method for making a soft magnetic film according to the present invention comprises electroplating an FeXCoYxcex1Z alloy film wherein xcex1 is at least one element selected from the group consisting of Rh, Pd, Pt, Ru, and Ir, the ratio X/Y by mass percent of Fe to Co is in the range of 2 to 5, and the xcex1 content Z is in the range of 0.5 to 18 mass percent, and X+Y+Z=100 mass percent.
In the present invention, the electroplating may be performed using a continuous DC current or a pulsed current. A pulsed current is preferable in the present invention.
That is, the FeCoxcex1 alloy layer is preferably formed by electroplating using a pulsed current in the present invention. In electroplating using a pulsed current, an operation time for energizing the system and a dead time for suspending the energizing are repeated during the plating process, for example, by ON/OFF switching using a current control element. By introducing the dead time, the FeXCoYxcex1Z alloy film is gradually deposited during the plating process, and the current density in the system becomes more uniform compared with plating by a continuous DC.
According to the method of the present invention, The FeXCoYxcex1Z alloy film prepared by the electroplating has the following composition: the ratio X/Y by mass percent of Fe to Co is in the range of 2 to 5, and the xcex1 content Z is in the range of 0.5 to 18 mass percent, and X+Y+Z=100 mass percent. This soft magnetic film exhibits a saturation magnetic flux density Bs of at least 2.0 T and higher corrosion resistance compared with an FeCo alloy not containing the element xcex1.
Preferably, the ratio X/Y by mass percent of Fe to Co is in the range of 2.6 to 4.3 and the xcex1 content Z is in the range of 3 to 9 mass percent. The soft magnetic film having such a composition exhibits a saturation magnetic flux density Bs of at least 2.2 T and higher corrosion resistance compared with a FeCo alloy not containing the element xcex1.
The FeXCoYxcex1Z alloy film is electroplated in a plating bath in which the Fe ion concentration is in the range of 1.2 to 3.2 g/liter, the Co ion concentration is in the range of 0.86 to 1.6 g/liter, and the xcex1 ion concentration is in the range of 0.2 to 6 mg/liter.
By controlling these ion concentrations, the ratio X/Y of Fe to Co can be set within the range of 2 to 5 and preferably 2.6 to 4.3, and the xcex1 content Z can be set within the range of 0.5 to 18 mass percent and preferably 3 to 9 mass percent in the plated FeXCoYxcex1Z alloy.
Preferably, the soft magnetic film further comprises an element xcex2 wherein xcex2 is at least one of Ni and Cr, the composition thereby being represented by the formula FeXCoYxcex1Zxcex2V, wherein the xcex2 content V is in the range of 0.5 to 5 mass percent and X+Y+Z+V=100 mass percent.
Preferably, the plating bath further contains sodium saccharine. Sodium saccharine functions as a stress relaxant to decrease the film stress of the plated FeCoxcex1 or FeCoxcex1xcex2 alloy.
Alternatively, the plating bath composition for forming the FeCoxcex1 or FeCoxcex1xcex2 alloy may contain 2-butyne-1,4-diol. This compound suppresses coarsening of the crystal grains in the plated alloy. As a result, voids between crystal grains decrease and thus the film has a smooth surface, resulting in a decreased coercive force Hc of the alloy.
Alternatively, the plating bath composition for forming the FeCoxcex1 or FeCoxcex1xcex2 alloy may contain sodium 2-ethylhexyl sulfate. Sodium 2-ethylhexyl sulfate being a surfactant removes hydrogen, which is generated during the plating process for forming the FeCoxcex1 or FeCoxcex1xcex2 alloy. Thus, this compound prevents the formation of a rough surface, which is caused by hydrogen trapped on the plated film.
Sodium 2-ethylhexyl sulfate may be replaced with sodium laurylsulfate; however, bubbling readily occurs in the plating bath containing sodium laurylsulfate compared with the plating bath containing sodium 2-ethylhexyl sulfate. Thus, it is difficult to determine the content of sodium laurylsulfate not causing bubbling. Accordingly, sodium 2-ethylhexyl sulfate, which barely causes bubbling, is preferably added in an amount which can effectively remove hydrogen.
In a method according to the present invention for making a thin-film magnetic head comprising a magnetic lower core layer, an upper core layer formed on the magnetic lower core layer with a magnetic gap provided therebetween, a coil layer for applying a recording magnetic field to the lower core layer and the upper core layer, at least one of the lower core layer and the upper core layer comprising a soft magnetic film, the method is characterized in that the soft magnetic film is formed by the above-described method.
Preferably, a lower magnetic pole layer is formed on the lower core layer at a face opposing a recording medium by plating so as to protrude on the lower core layer, and the lower magnetic pole layer comprises the soft magnetic film.
In a method according to the present invention for making a thin-film magnetic head having a lower core layer, an upper core layer, and a magnetic pole unit provided between the lower core layer and the upper core layer, the length of the magnetic pole unit being shorter than that of the lower core layer and the upper core layer in the track width direction, the magnetic pole unit including a lower magnetic pole layer in contact with the lower core layer, an upper magnetic pole layer in contact with the upper core layer, and a gap layer lying between the lower magnetic pole layer and the upper magnetic pole layer, or including an upper magnetic pole layer in contact with the upper core layer and a gap layer lying between the upper magnetic pole layer and the lower core layer, the method comprises forming at least one of the upper magnetic pole layer and the lower magnetic pole layer by the above-described method, at least one of the upper magnetic pole layer and the lower magnetic pole layer thereby comprising the soft magnetic film.
Preferably, the upper magnetic pole layer comprises the soft magnetic film, and the upper core layer is formed on the upper magnetic pole layer by electroplating a NiFe alloy.
Preferably, at least one of the upper core layer and the lower core layer includes at least two sublayers at least at a portion adjacent to the magnetic gap or at least one of the upper magnetic pole layer and the lower magnetic pole layer includes at least two magnetic sublayers, the magnetic sublayer in contact with the magnetic gap comprising the soft magnetic film.
Preferably, the magnetic sublayer which is not in contact with the magnetic gap is formed by plating a NiFe alloy.
The soft magnetic film which is formed by electroplating an FeCoxcex1 alloy or an FeCoxcex1xcex2 alloy have a composition FeXCoYxcex1Z wherein xcex1 is at least one element selected from the group consisting of Rh, Pd, Pt, Ru, and Ir, the ratio X/Y by mass percent of Fe to Co is in the range of 2 to 5 and preferably 2.6 to 4.3, the xcex1 content Z is in the range of 0.5 to 18 mass percent and preferably 3 to 9 mass percent, and X+Y+Z=100 mass percent, or a composition FeXCoYxcex1Zxcex2V wherein xcex2 is at least one of Ni and Cr, the ratio X/Y by mass percent of Fe to Co is in the range of 2 to 5 and more preferably in the range of 2.6 to 4.3, the xcex1 content Z is in the range of 0.5 to 18 mass percent and more preferably in the range of 3 to 9 mass percent, the xcex2 content V is in the range of 0.5 to 5 mass percent, and X+Y+Z+V=100 mass percent.
A thin-film magnetic head including a core layer composed of such a soft magnetic film can be readily produced with high yield. The resulting thin-film magnetic head has a saturation magnetic flux density BS which is suitable for high-recording density and has higher corrosion resistance compared with an FeCo alloy not containing the element xcex1.